The present invention relates to the field of devices for determining fluid flow rates. More particularly, but not exclusively, it relates to a device for determining flow rates of gases in anesthetic ventilators.
Many forms of equipment require a flow rate of liquids, gases or vapors through the equipment to be measured, whether purely for recording purposes or so that deviations from a desired fluid flow rate may be identified and corrected. A wide range of flow rate measuring devices are known, but many are suitable only for a limited range of fluid viscosities and cannot easily be adjusted for use with fluids having viscosities outside this range.
For example, in the field of anesthetic ventilators, a general idea of flow rates can be obtained by passing a carrier gas or vapor flow through a restricted orifice and determining a pressure drop across the orifice. However, this approach has been found to be insufficiently reliable. For example, the exact configuration and size of the orifice can be critical, leading to poor reproductibility between different units of apparently identical design. A particular orifice size is only effective for a particular, usually narrow, range of fluid viscosities. Additionally, flow through such an orifice can become non-linear or even turbulent at high fluid flow rates, and a restricted orifice may also significantly restrict the fluid flow rates that it is intended to measure.
Similar issues are believed to apply to other fluid flow measuring devices in a range of different fields, working with a range of different fluids.
It is hence an object of the present invention to provide a fluid flow sensing and measuring device that has greater flexibility and adaptability than existing devices, and which obviates some or all of the above drawbacks of existing devices.